Studies are continuing of the several human peripheral lymphocyte sub-populations separated by column fractionation and sedimentation techniques and of their role in the development and expression of delayed hypersensitivity reactions. Studies are also currently in progress to determine if transfer factor is elaborated by one or several of these lymphocyte sub-populations. In vitro systems for the estimation of transfer factor are also being assessed but the results to date have been inconsistent and not promising. Clinical trials of transfer factor in the therapy of several immunologic deficiency syndromes are continuing. The relationship of development of cell-mediated delayed hypersensitivity to the development of reaginic antibody (IgE) synthesis is currently being examined in inbred BN and ACI rats. It appears that reaginic antibody synthesis precedes the development of cell mediated immune response by 3 to 7 days and persists longer. Studies of the development and mechanisms of hypersensitivity in severe asthmatic patients have shown that certain asthmatic children respond to repeated antigenic stimulation with increased serum IgM synthesis in addition to increased serum IgE synthesis but the mechanism of this response is not apparent. We have confirmed our previous observation that severe asthmatics after receiving catecholamines have decreased urinary cyclic AMP as compared to normals and have better defined these patients' responses in prospective studies.